Cummins ISB CM550 (1990-94) Fault Code: 143-SW PID: 100 SPN: 100 FMI: 1 Oil Pressure Switch Circuit

Posted by PerDiezel Solutions on January 16, 2026

Circuit Description
The oil pressure switch is used by the engine control module (ECM) to detect the presence of
lubricating oil pressure.

Component Location
The oil pressure switch is located on the engine block, below and to the right of the ECM.

Shop Talk
1) Confirm that the oil pressure sensor supply voltage is between (+) 4.5 and 5.25-VDC at
the sensor.
2) Verify, with the driver, the engine speed at which the fault occurs. If the engine is being
operated at too low of a speed under load, the oil pressure can drop below the engine
protection limits.
3) Connect a manual gauge to monitor the actual oil pressure of the engine.
4) The fault will trigger if lubricating oil pressure drops below 41 kPa [6 psi] for 5 seconds
while the engine is operating.
5) Engines in the field can have had a jumper harness kit installed which connect the oil pressure switch to pin K in the 23-pin OEM connector or cavity 8 in the Ford original equipment manufacturer (OEM) connector.

Cummins ISB CM550 (1990-94) Fault Code: 143-SN PID: 100 SPN: 100 FMI: 1 Oil Pressure Switch Circuit

Cummins ISB CM550 (1990-94) Fault Code: 141-SW PID: 100 SPN: 100 FMI: 4 Oil Pressure Switch Circuit

Cummins ISB CM550 (1990-94) Fault Code: 141-SN PID: 100 SPN: 100 FMI: 4 Oil Pressure Sensor Circuit

Cummins ISB CM550 (1990-94) Fault Code: 135 PID: 100 SPN: 100 FMI: 3 Oil Pressure Sensor Circuit

Cummins ISB CM550 (1990-94) Fault Code: 134 PID: 29 SPN: 29 FMI: 4 Remote Throttle Position Sensor

Cummins ISB CM550 (1990-94) Fault Code: 133 PID: 29 SPN: 29 FMI: 3 Remote Throttle Position Sensor

WARNING!